Article

Past Problems Of Turbines Which Led To Technology Advances

by Neville F. Rieger

ABSTRACT

This paper reads as a history of how our understanding of machine problems such as critical speeds, oil whirl, oil whip and other forms of instabilities were developed. Most of this knowledge was developed many years ago as a result of machine failures that at the time could not be fully explained. Root cause failure analysis investigations were essentially performed on each type of failure by companies, research organizations, and in some cases government agencies to better understand the causes. In most cases models of the machines were fabricated and tested under similar conditions to duplicate the instabilities. This approach allowed detailed observations by researchers, better understanding of the problems, and eventual recommendations on how to best avoid these problems thru improved design and operation. Reading this paper made me appreciate even more those in the past that increased our knowledge so much in the field of rotor dynamics. It was interesting to me that in most cases experimental observations and general recommendations from these observations came first; theoretical explanation of them was developed after the observations had been made – this is the essence of the scientific method.

PREVIEW

“Introduction:

This paper contains a short discussion of four major rotating machinery problems, each of which resulted in some significant advance in the technical knowledge of the problem area involved. None of the problems described could be solved when the problem first occurred, because fundamental knowledge of the causal mechanism was then lacking. The knowledge required to solve the immediate problem was obtained from studies made in the course of the problem solution. It was subsequently found that each problem area represented a major area of technology, each of which has subsequently developed into an aspect of the science of rotordynamics.

Problem 1: Rotordynamics of Shaft Systems

Rankine [1] made the first dynamical studies of a uniform rotating shaft supported in radially-stiff end bearings in 1869. The concept and calculation involved led Rankine to conclude that beyond a certain limiting speed the shaft would become unstable, and its amplitude would increase without limit (much like a buckling column). Rankine named this the “critical speed.” Rankine died in 1871, but further work on the critical speed concept was added by Greenhill [2] in 1883, who investigated the combined influence of centrifugal force, axial thrust, and drive torque on the critical (buckling) speed of long marine screw propulsion shafts, which were being developed with the rapid evolution of naval vessels at that time. This era of the reaction steam turbine coincides with the invention of the impulse steam turbine by Laval (1883-1893) in Sweden, and by Parsons (1884-1897) in England. Developments in bearings and lubrication were also made during this period by Tower (1883), Reynolds (1885), and later by Sommerfeld (1903) and Michell (1905). Direct-current dynamos driven by reciprocating steam engines were introduced on an industrial scale around 1880-1885 by Edison and others, while alternating-current machinery made its appearance around 1889-1892, promoted by Tesla and Westinghouse, who applied Parsons’ industrial steam turbine as the prime mover for their alternators in New York and Philadelphia in 1891.Dunkerley [3] in 1895 greatly extended practical knowledge of critical speeds of shafting systems by publishing the results of extensive theoretical and experimental studies (with contributions by 0. Reynolds) on many arrangements of flexible shafts in radially-stiff bearings, and carrying pulleys. These studies were consolidated into a convenient approximate procedure for estimating the lowest critical speeds of complex systems of shafts, pulleys, and bearings, which came to be known as ‘Dunkerley’s Method.'”

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